WIP: Query by pairs of values

[amitaibu]

I'm trying to query records by pair of values.

I have these projects:

Let's say I want to fetch only the records that have
(ProjectTypeOngoing, 2) and (ProjectTypeNotStarted, 3)

You can grab this PR, make db and go to http://localhost:8000/Projects

[amitaibu]

Here's the query. It compiles, but isn't right:

[amitaibu]

I tried to implement ToField:

instance ToField (ProjectType, Text) where
    toField (projectType, participants) = Many [toField projectType, toField participants]


instance Controller ProjectsController where
    action ProjectsAction = do
        projects <- query @Project |> fetch

        -- Fetch only specific projects by a pair of values.
        -- In this case we really fetch all, but show how we pair the values we want to
        -- query by.
        let pairs = projects |> fmap (\project -> (project.projectType, project.participants))

        -- Use a parameterized query to handle list of tuples
        projectsQuery :: [Project] <- sqlQuery "SELECT * FROM projects WHERE (project_type, participants) IN ?" (Only $ In pairs)


        render IndexView { .. }

But this now has this error